«7* 



ON THE OXIDES OF IRON* 



whence it will follow^ that 100 parts of black oxide of iroH 

 ari^ composed in round numbers of 76 iron and 24 oxigen. 

 White oxide. ,N 9, method of obtaining the white oxide of iron is yet 

 known, but tliat of dissolving the metal in an acid. When 

 the oxide thus obtained is precipitated, it immediately com- 

 bines with oxii^en to v^encrate black oxide, and frequently 

 red oxid« ; so that we have no method of finding the propor^ 

 tion of oxigen in white oxide but by calculating from the 

 bjdrogen gas evolved during the solution. 



in tliis way we found the proportion of oxigen to vary be- 

 tween 2t>*6 and 30. To choose between these two numbers, 

 taken from the experiments of Vauqnelin, we should know 

 the state of the iron d»jsolv:ed, and the mode in which the 

 solution was conducted. Calculating from the ditferent de- 

 grees of impurity io iron, we shall be led totidopt the pro- 

 portion of 30 ; yet, I think, it vvould be preferable to take 

 jthat of 29 of oxigen to 100 of iron, deduced from the expe- 

 riments of the French academicians, Monge, Vandermonde, 

 and Berthollet: because, 1st, it was the highest product 

 they obtained from 21 varieties of good iron, which they 

 dissolved: 2dly, they were particularly careful in measuring 

 the gasses they obtained; 3d!y, they reduced these mea- 

 sures to a uniform temperature and pressure, whence it was 

 easy to calculate the exact quantity of oxigen correspond- 

 ing ; 4thly, in the experiment of Vauquelin, which may be 

 considered as very accurate, the omission of the temperature 

 and pressure, at which the gasses were obtained, renders us 

 unable to compute exactly the quantity of oxigen. 

 ■5 ifonto From these considerations it follows, that the white oxidr 



is composed of very nearly 29 parts of oxigen to 100 of iron ; 

 and that 100 parts of white oxide contain 77*5 iron and 22*5 



oxigen. 



Addition, 



Difference be- , ]VIineralQgistsknow,thatthereare very characteristic dijffer- 



iween the na- ^.^j^es between the oxiduleof iron of the valley of Aost, which 



tive oxides ox i r • i i j 



Aost and Elba, the celebrated Ilai'iy designates under the nameof oxidulated 



iron, and the oxidule of the isle of Elba, which he calls oli- 



gist Iron. The primitive form of the first is the octaedron, 



and it yieUU ablaek powdej' ; the primitive form of the second 



* sa rhomboid, souiewhal acute, and it yields a red powder. 



T esc two oxidules appear to differ in the former being 



*lv*«)*^*» only 



22 5 oxigen. 



